/**
   * Removes obsolete deployments in case of redeploy.
   *
   * @param meta Request metadata.
   * @return List of shares deployment.
   */
  private GridTuple2<Boolean, SharedDeployment> checkRedeploy(GridDeploymentMetadata meta) {
    assert Thread.holdsLock(mux);

    SharedDeployment newDep = null;

    for (List<SharedDeployment> deps : cache.values()) {
      for (SharedDeployment dep : deps) {
        if (!dep.isUndeployed() && !dep.isPendingUndeploy()) {
          long undeployTimeout = ctx.config().getNetworkTimeout();

          SharedDeployment doomed = null;

          // Only check deployments with no participants.
          if (!dep.hasParticipants()) {
            // In case of SHARED deployment it is possible to get hear if
            // unmarshalling happens during undeploy. In this case, we
            // simply don't do anything.
            if (dep.deployMode() == CONTINUOUS) {
              if (dep.existingDeployedClass(meta.className()) != null) {
                // Change from shared deploy to shared undeploy or user version change.
                // Simply remove all deployments with no participating nodes.
                if (meta.deploymentMode() == SHARED
                    || !meta.userVersion().equals(dep.userVersion())) doomed = dep;
              }
            }
          }
          // If there are participants, we undeploy if class loader ID on some node changed.
          else if (dep.existingDeployedClass(meta.className()) != null) {
            GridTuple2<GridUuid, Long> ldr = dep.getClassLoaderId(meta.senderNodeId());

            if (ldr != null) {
              if (!ldr.get1().equals(meta.classLoaderId())) {
                // If deployed sequence number is less, then schedule for undeployment.
                if (ldr.get2() < meta.sequenceNumber()) {
                  if (log.isDebugEnabled())
                    log.debug(
                        "Received request for a class with newer sequence number "
                            + "(will schedule current class for undeployment) [newSeq="
                            + meta.sequenceNumber()
                            + ", oldSeq="
                            + ldr.get2()
                            + ", senderNodeId="
                            + meta.senderNodeId()
                            + ", newClsLdrId="
                            + meta.classLoaderId()
                            + ", oldClsLdrId="
                            + ldr.get1()
                            + ']');

                  doomed = dep;
                } else if (ldr.get2() > meta.sequenceNumber()) {
                  long time = System.currentTimeMillis() - dep.timestamp();

                  if (newDep == null && time < ctx.config().getNetworkTimeout()) {
                    // Set undeployTimeout, so the class will be scheduled
                    // for undeployment.
                    undeployTimeout = ctx.config().getNetworkTimeout() - time;

                    if (log.isDebugEnabled())
                      log.debug(
                          "Received execution request for a stale class (will deploy and "
                              + "schedule undeployment in "
                              + undeployTimeout
                              + "ms) "
                              + "[curSeq="
                              + ldr.get2()
                              + ", staleSeq="
                              + meta.sequenceNumber()
                              + ", cls="
                              + meta.className()
                              + ", senderNodeId="
                              + meta.senderNodeId()
                              + ", curLdrId="
                              + ldr.get1()
                              + ", staleLdrId="
                              + meta.classLoaderId()
                              + ']');

                    // We got the redeployed class before the old one.
                    // Simply create a temporary deployment for the sender node,
                    // and schedule undeploy for it.
                    newDep = createNewDeployment(meta, false);

                    doomed = newDep;
                  } else {
                    U.warn(
                        log,
                        "Received execution request for a class that has been redeployed "
                            + "(will ignore): "
                            + meta.alias());

                    if (log.isDebugEnabled())
                      log.debug(
                          "Received execution request for a class that has been redeployed "
                              + "(will ignore) [alias="
                              + meta.alias()
                              + ", dep="
                              + dep
                              + ']');

                    return F.t(false, null);
                  }
                } else {
                  U.error(
                      log,
                      "Sequence number does not correspond to class loader ID [seqNum="
                          + meta.sequenceNumber()
                          + ", dep="
                          + dep
                          + ']');

                  return F.t(false, null);
                }
              }
            }
          }

          if (doomed != null) {
            doomed.onUndeployScheduled();

            if (log.isDebugEnabled()) log.debug("Deployment was scheduled for undeploy: " + doomed);

            // Lifespan time.
            final long endTime = System.currentTimeMillis() + undeployTimeout;

            // Deployment to undeploy.
            final SharedDeployment undep = doomed;

            ctx.timeout()
                .addTimeoutObject(
                    new GridTimeoutObject() {
                      @Override
                      public GridUuid timeoutId() {
                        return undep.classLoaderId();
                      }

                      @Override
                      public long endTime() {
                        return endTime < 0 ? Long.MAX_VALUE : endTime;
                      }

                      @Override
                      public void onTimeout() {
                        boolean removed = false;

                        // Hot redeployment.
                        synchronized (mux) {
                          assert undep.isPendingUndeploy();

                          if (!undep.isUndeployed()) {
                            undep.undeploy();

                            undep.onRemoved();

                            removed = true;

                            Collection<SharedDeployment> deps = cache.get(undep.userVersion());

                            if (deps != null) {
                              for (Iterator<SharedDeployment> i = deps.iterator(); i.hasNext(); )
                                if (i.next() == undep) i.remove();

                              if (deps.isEmpty()) cache.remove(undep.userVersion());
                            }

                            if (log.isInfoEnabled())
                              log.info(
                                  "Undeployed class loader due to deployment mode change, "
                                      + "user version change, or hot redeployment: "
                                      + undep);
                          }
                        }

                        // Outside synchronization.
                        if (removed) undep.recordUndeployed(null);
                      }
                    });
          }
        }
      }
    }

    if (newDep != null) {
      List<SharedDeployment> list =
          F.addIfAbsent(cache, meta.userVersion(), F.<SharedDeployment>newList());

      assert list != null;

      list.add(newDep);
    }

    return F.t(true, newDep);
  }
  /** {@inheritDoc} */
  @Override
  public GridDeployment getDeployment(GridDeploymentMetadata meta) {
    assert meta != null;

    assert ctx.config().isPeerClassLoadingEnabled();

    // Validate metadata.
    assert meta.classLoaderId() != null;
    assert meta.senderNodeId() != null;
    assert meta.sequenceNumber() >= -1;
    assert meta.parentLoader() == null;

    if (log.isDebugEnabled())
      log.debug("Starting to peer-load class based on deployment metadata: " + meta);

    while (true) {
      List<SharedDeployment> depsToCheck = null;

      SharedDeployment dep = null;

      synchronized (mux) {
        // Check obsolete request.
        if (isDeadClassLoader(meta)) return null;

        List<SharedDeployment> deps = cache.get(meta.userVersion());

        if (deps != null) {
          assert !deps.isEmpty();

          for (SharedDeployment d : deps) {
            if (d.hasParticipant(meta.senderNodeId(), meta.classLoaderId())
                || meta.senderNodeId().equals(ctx.localNodeId())) {
              // Done.
              dep = d;

              break;
            }
          }

          if (dep == null) {
            GridTuple2<Boolean, SharedDeployment> redeployCheck = checkRedeploy(meta);

            if (!redeployCheck.get1()) {
              // Checking for redeployment encountered invalid state.
              if (log.isDebugEnabled())
                log.debug("Checking for redeployment encountered invalid state: " + meta);

              return null;
            }

            dep = redeployCheck.get2();

            if (dep == null) {
              // Find existing deployments that need to be checked
              // whether they should be reused for this request.
              for (SharedDeployment d : deps) {
                if (!d.isPendingUndeploy() && !d.isUndeployed()) {
                  if (depsToCheck == null) depsToCheck = new LinkedList<SharedDeployment>();

                  if (log.isDebugEnabled()) log.debug("Adding deployment to check: " + d);

                  depsToCheck.add(d);
                }
              }

              // If no deployment can be reused, create a new one.
              if (depsToCheck == null) {
                dep = createNewDeployment(meta, false);

                deps.add(dep);
              }
            }
          }
        } else {
          GridTuple2<Boolean, SharedDeployment> redeployCheck = checkRedeploy(meta);

          if (!redeployCheck.get1()) {
            // Checking for redeployment encountered invalid state.
            if (log.isDebugEnabled())
              log.debug("Checking for redeployment encountered invalid state: " + meta);

            return null;
          }

          dep = redeployCheck.get2();

          if (dep == null)
            // Create peer class loader.
            dep = createNewDeployment(meta, true);
        }
      }

      if (dep != null) {
        if (log.isDebugEnabled())
          log.debug("Found SHARED or CONTINUOUS deployment after first check: " + dep);

        // Cache the deployed class.
        Class<?> cls = dep.deployedClass(meta.className(), meta.alias());

        if (cls == null) {
          U.warn(
              log,
              "Failed to load peer class (ignore if class got undeployed during preloading) [alias="
                  + meta.alias()
                  + ", dep="
                  + dep
                  + ']');

          return null;
        }

        return dep;
      }

      assert meta.parentLoader() == null;
      assert depsToCheck != null;
      assert !depsToCheck.isEmpty();

      /*
       * Logic below must be performed outside of synchronization
       * because it involves network calls.
       */

      // Check if class can be loaded from existing nodes.
      // In most cases this loop will find something.
      for (SharedDeployment d : depsToCheck) {
        // Load class. Note, that remote node will not load this class.
        // The class will only be loaded on this node.
        Class<?> cls = d.deployedClass(meta.className(), meta.alias());

        if (cls != null) {
          synchronized (mux) {
            if (!d.isUndeployed() && !d.isPendingUndeploy()) {
              if (!addParticipant(d, meta)) return null;

              if (log.isDebugEnabled())
                log.debug(
                    "Acquired deployment after verifying it's availability on "
                        + "existing nodes [depCls="
                        + cls
                        + ", dep="
                        + d
                        + ", meta="
                        + meta
                        + ']');

              return d;
            }
          }
        } else if (log.isDebugEnabled()) {
          log.debug(
              "Deployment cannot be reused (class does not exist on participating nodes) [dep="
                  + d
                  + ", meta="
                  + meta
                  + ']');
        }
      }

      // We are here either because all participant nodes failed
      // or the class indeed should have a separate deployment.
      for (SharedDeployment d : depsToCheck) {
        // Temporary class loader.
        ClassLoader temp =
            new GridDeploymentClassLoader(
                GridUuid.randomUuid(),
                meta.userVersion(),
                meta.deploymentMode(),
                true,
                ctx,
                ctxLdr,
                meta.classLoaderId(),
                meta.senderNodeId(),
                meta.sequenceNumber(),
                comm,
                ctx.config().getNetworkTimeout(),
                log,
                ctx.config().getPeerClassLoadingClassPathExclude(),
                0,
                false);

        String path = U.classNameToResourceName(d.sampleClassName());

        // We check if any random class from existing deployment can be
        // loaded from sender node. If it can, then we reuse existing
        // deployment.
        InputStream rsrcIn = temp.getResourceAsStream(path);

        if (rsrcIn != null) {
          // We don't need the actual stream.
          U.closeQuiet(rsrcIn);

          synchronized (mux) {
            if (d.isUndeployed() || d.isPendingUndeploy()) continue;

            // Add new node prior to loading the class, so we attempt
            // to load the class from the latest node.
            if (!addParticipant(d, meta)) {
              if (log.isDebugEnabled())
                log.debug(
                    "Failed to add participant to deployment "
                        + "[meta="
                        + meta
                        + ", dep="
                        + dep
                        + ']');

              return null;
            }
          }

          Class<?> depCls = d.deployedClass(meta.className(), meta.alias());

          if (depCls == null) {
            U.error(
                log,
                "Failed to peer load class after loading it as a resource [alias="
                    + meta.alias()
                    + ", dep="
                    + dep
                    + ']');

            return null;
          }

          if (log.isDebugEnabled())
            log.debug(
                "Acquired deployment class after verifying other class "
                    + "availability on sender node [depCls="
                    + depCls
                    + ", rndCls="
                    + d.sampleClass()
                    + ", sampleClsName="
                    + d.sampleClassName()
                    + ", meta="
                    + meta
                    + ']');

          return d;
        } else if (log.isDebugEnabled())
          log.debug(
              "Deployment cannot be reused (random class could not be loaded from sender node) [dep="
                  + d
                  + ", meta="
                  + meta
                  + ']');
      }

      synchronized (mux) {
        if (log.isDebugEnabled())
          log.debug(
              "None of the existing class-loaders fit (will try to create a new one): " + meta);

        // Check obsolete request.
        if (isDeadClassLoader(meta)) return null;

        // Check that deployment picture has not changed.
        List<SharedDeployment> deps = cache.get(meta.userVersion());

        if (deps != null) {
          assert !deps.isEmpty();

          boolean retry = false;

          for (SharedDeployment d : deps) {
            // Double check if sender was already added.
            if (d.hasParticipant(meta.senderNodeId(), meta.classLoaderId())) {
              dep = d;

              retry = false;

              break;
            }

            // New deployment was added while outside of synchronization.
            // Need to recheck it again.
            if (!d.isPendingUndeploy() && !d.isUndeployed() && !depsToCheck.contains(d))
              retry = true;
          }

          if (retry) {
            if (log.isDebugEnabled()) log.debug("Retrying due to concurrency issues: " + meta);

            // Outer while loop.
            continue;
          }

          if (dep == null) {
            // No new deployments were added, so we can safely add ours.
            dep = createNewDeployment(meta, false);

            deps.add(dep);

            if (log.isDebugEnabled())
              log.debug(
                  "Adding new deployment within second check [dep=" + dep + ", meta=" + meta + ']');
          }
        } else {
          dep = createNewDeployment(meta, true);

          if (log.isDebugEnabled())
            log.debug(
                "Created new deployment within second check [dep=" + dep + ", meta=" + meta + ']');
        }
      }

      if (dep != null) {
        // Cache the deployed class.
        Class<?> cls = dep.deployedClass(meta.className(), meta.alias());

        if (cls == null) {
          U.warn(
              log,
              "Failed to load peer class (ignore if class got undeployed during preloading) [alias="
                  + meta.alias()
                  + ", dep="
                  + dep
                  + ']');

          return null;
        }
      }

      return dep;
    }
  }